Aerodynamics is the science of how air flows around and inside objects. More generally, it can be labeled “Fluid Dynamics” because air is really just a very thin type of fluid. Above slow speeds, the air flow around and through a motor vehicle begins to have a more pronounced effect on the acceleration, top speed, fuel efficiency and handling. Therefore, it is necessary to understand and optimize how the air flows around and through the motor vehicle, its openings and its aerodynamic devices, as aerodynamics play a big role on the overall build of motor vehicles. The aerodynamics of motor vehicles are designed for reducing drag, wind noise, minimizing noise emission, preventing undesired lift forces, bringing down CO2 emissions and other causes of aerodynamic instability at high speeds.
To understand the full aerodynamic effect of a motor vehicle, we need to take into account the frontal area of the vehicle. The frontal area defines the size of the hole the vehicle makes in the air as it drives through it. And thus a frontal pressure effect is created, or the effect created by a vehicle body pushing air out of the way. The Frontal pressure is caused by the air attempting to flow around the front of the vehicle. As millions of air molecules approach the front of the car, they begin to compress, and in doing so raise the air pressure in front of the car. At the same time, the air molecules travelling along the sides of the car are at atmospheric pressure, a lower pressure compared to the molecules at the front of the car. Just like an air tank, if the valve to the lower pressure atmosphere outside the tank is opened, the air molecules will naturally flow to the lower pressure area, eventually equalizing the pressure inside and outside the tank. The same rules apply to any vehicle. The compressed molecules of air naturally seek a way out of the high pressure zone in front of the vehicle, and they find it around the sides, top and bottom of the motor vehicle.
According to Bernoulli's principle, for a given volume of air, the higher the velocity the air molecules are travelling, the lower the pressure becomes. Likewise, for a given volume of air, the lower the velocity of the air molecules, the higher the pressure becomes. This applies to air in motion across a still body, or to a motor vehicle in motion, moving through relatively still air. In the frontal pressure section above, we said that the air pressure was high as the air rammed into the front grill of the car. What is happening is that the air slows down as it approaches the front of the car, and as a result more molecules are packed into a smaller space. Once the air stagnates at the point in front of the car, it seeks a lower pressure area, such as the sides, top and bottom of the car.
Additionally, a underside of the motor vehicle is also responsible for creating lift or downforce. If a motor vehicle's front end is lower than the rear end, then the front end restricts the air flow under the car and the widening gap between the underside and the road creates a low pressure area. If there is neutral or higher air pressure above the car, then we get downforce due to the difference in the pressure above and below the car. Therefore, an air dam at the front of the motor vehicle may restrict the flow of air reaching the underside of the car. The air dam does this by creating a “dam” or wall across the front of the motor vehicle that extends close down to the road and creates an area of vacuum or low pressure underneath the motor vehicle. This low pressure area, in combination with the higher pressures above the front and top of the vehicle, effectively generates downforce at the front of the vehicle. In many cases, the air dam also reduces the Coefficient of Drag (Cd) of the vehicle. Cd is a dimensionless value well known to those skilled in the art to enable the comparison of the drag produced by one motor vehicle versus another. Every motor vehicle has a Cd which can be measured using wind tunnel data. The Cd can be used in drag equations to determine the drag force at various speeds.
With new regulations for new motor vehicles requiring a reduction of the CO2 emissions, front end aerodynamics play key role in bringing down CO2 emissions on motor vehicles. As seen by FIG. 1, the prior art shows a motor vehicle 1 with a front end 2 having an air dam 3. Furthermore, the air dam 3 is attached to be fixed at one spot below the front end 2 making the air dam 3 non-movable. Typically, the air dam 3 is made of up one piece plastic and reduces a ground clearance 4 of the motor vehicle 1. Often, this may result in scraping of the air dam 3 on the pavement during parking and severe damage during off-roading since angle of approach is reduced significantly. Further seen by FIG. 1, the motor vehicle 1 is a truck, however, the motor vehicle 1 may also be understood to be a car, sport utility vehicle or suburban utility vehicle (SUV), or any known automobile in the art.